1. Field of the Invention
The present invention relates to a thin film magnetic head. Specifically, the present invention relates to the device structure of a thin film magnetic head having a magnetoresistance effect element (MR element) that includes a layer containing Zn at the interface between a magnetic layer and a non-magnetic intermediate layer.
2. Description of the Related Art
As the high recording density of a hard disk drive (HDD) has been developed, heads of high sensitivity and high output have been required. A spin valve head was invented as a head that satisfies the aforementioned requirements. A spin valve head is provided with a pair of ferromagnetic layers on both sides of a non-magnetic intermediate layer. An antiferromagnetic layer is disposed in contact with one ferromagnetic layer, and the magnetization direction of the ferromagnetic layer is fixed in one direction by means of exchange coupling with the antiferromagnetic layer. The magnetization direction of the other ferromagnetic layer freely rotates according to an external magnetic field. Such a ferromagnetic layer is referred to as a free layer. In a spin valve head, the change in the relative angle of spins in these two ferromagnetic layers brings about the change in the magnetoresistance.
A spin valve structure is not always required to obtain a large magnetoresistance ratio (MR ratio) for high sensitivity and high output, but the electric resistance according to the change in the relative angle of spins must be greatly changed. In order to achieve this, it is important that oxidation of a magnetic layer is prevented, and a spin polarizability of the magnetic layer is not decreased by a layer adjacent to the magnetic layer. Specifically, when a giant magnetoresistance (GMR) effect is utilized by using a semiconductor material as a non-magnetic intermediate layer sandwiched by magnetic layers, a large MR ratio is expected. However, at the same time, it is necessary that an influence of a non-magnetic intermediate layer made of oxide upon a magnetic layer is kept as small as possible.
It is well known that a non-magnetic metal layer is formed at the interface between a non-magnetic intermediate layer and a magnetic layer to reduce the magnetic characteristic degradation of the magnetic layer. For example, Japanese laid-open patent application number 2008-124173 discloses that, in a structure in which two magnetic layers sandwich a non-magnetic intermediate layer made of ZnO, an intermediate interface layer made of Zn is sandwiched at each of the interfaces between the magnetic layer and the non-magnetic intermediate layer. According to the layer structure described above, since an influence of the non-magnetic intermediate layer upon the magnetic layer is decreased, it is expected to have a large MR ratio due to the layer structure compared with a structure that a non-magnetic intermediate layer and a magnetic layer directly contact each other. However, such a large MR ratio is vastly decreased after an annealing process that is always required during manufacturing processes. This is because Zn and O atoms are diffused from a non-magnetic intermediate layer to a magnetic layer even though through an intermediate interface layer; and it is understood that Zn is further diffused from the intermediate interface layer that contacts the magnetic layer. Therefore, it is important that the heat resistance is considered for realizing reading heads of high sensitivity and high output in such a layer structure.